Ecological studies on the fauna associated with decaying logs and leaf-litter in New Zealand Pinus forests, with particular reference to the Coleoptera

Abstract

Ecological investigations were made of the fauna inhabiting decaying logs and leaf-litter in Pinus forests in New Zealand. Principal study areas were Powhaturoa Forest, Beachlands, Auckland; and Holmes Plantation, Burnham, Canterbury. Field studies were made at Auckland from 1966 to 1969, and at Burnham during 1970 and 1971. Old logs (aged about 9 years) contained the greatest abundance and diversity of animals; Collembola and Acarina occurred most frequently. No significant differences in faunal abundance in logs were found between winter and summer at Beachlands, but in the same seasons significant differences occurred at Burnham. Winter means were usually highest and summer means lowest at Burnham. A nested sub-sampling programme for logs showed highly significant (P<0.01) or greater differences existed, with all taxonomic groups, in the "logs with in seasons" category. Most groups also had significant differences in the "sections with in logs" category. Pitfall trapping of the Total fauna (excluding Acarina) showed most groups differed significantly in abundance among seasons. No consistent pattern among spring, summer and autumn occurred, although winter numbers were usually lowest. Three-way analysis of variance of Carabidae trapped showed highly significant differences among trapping areas, seasons, and species. Two first-order interactions (areas x species and seasons x species) were also highly significant. Analysis of the community sampled by pitfall trapping indicated two related associations and a third which was smaller and more distinct. Species comprising the first two groups were possibly associated mainly by predator/prey relationships, although some overlap of diurnally active and nocturnal species is possible. Utilisation of a common food resource (possibly fungi) may have associated members of the third group. Comparison of log heat extraction with pitfall trapping in winter and summer indicated most groups had significant differences between seasons and techniques. In winter a significantly higher proportion of Collembola and Araneida occurred in pitfall traps than logs. Significantly more Isopoda and Total Animals (excluding Collembola) occurred in logs. In summer, no significant differences occurred with any insect group between traps and logs. Emergence cage studies indicated few significant differences among the numbers of animals emerging from logs of moderate or advanced decay. Significant or greater differences were detected among sampling periods with some taxonomic groups. Many kinds of animals occurred under artificial sites. Acarina and Collembola were the most abundant; the former occurred more consistently, and the latter decreased markedly with the onset of dry summer conditions. Analysis of variance showed significant differences among sampling periods with most groups. Multiple range testing showed that usually no significant differences occurred between July, August, November and March. Significantly lower populations occurred in October, December and January. These periods corresponded with times of higher and lower rainfall and litter moisture. The Total Insects category occurred in significantly higher numbers during the colder but wetter months of July and August. It is concluded that the fauna inhabiting logs and leaf-litter in Pinus forests in New Zealand is abundant and diverse. Although most species are endemic, they live very successfully in the environment associated with the exotic trees.